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.. _2.1.3_c:

2.1.3 Touch Switch Module
====================================

Introduction
-------------------

In this project, you will learn about touch switch module. It can replace 
the traditional kinds of switch with these advantages: convenient operation, 
fine touch sense, precise control and least mechanical wear.


Required Components
------------------------------

In this project, we need the following components. 

.. image:: ../img/2.1.3component.png
    :width: 700
    :align: center

It's definitely convenient to buy a whole kit, here's the link: 

.. list-table::
    :widths: 20 20 20
    :header-rows: 1

    *   - Name	
        - ITEMS IN THIS KIT
        - LINK
    *   - Raphael Kit
        - 337
        - |link_Raphael_kit|

You can also buy them separately from the links below.

.. list-table::
    :widths: 30 20
    :header-rows: 1

    *   - COMPONENT INTRODUCTION
        - PURCHASE LINK

    *   - :ref:`cpn_gpio_extension_board`
        - |link_gpio_board_buy|
    *   - :ref:`cpn_breadboard`
        - |link_breadboard_buy|
    *   - :ref:`cpn_wires`
        - |link_wires_buy|
    *   - :ref:`cpn_resistor`
        - |link_resistor_buy|
    *   - :ref:`cpn_led`
        - |link_led_buy|
    *   - :ref:`cpn_touch_switch`
        - |link_touch_buy|

Schematic Diagram
-----------------

.. image:: ../img/2.1.3circuit.png
    :width: 500
    :align: center

Experimental Procedures
------------------------------

**Step 1:** Build the circuit.

.. image:: ../img/2.1.3fritzing.png
    :width: 700
    :align: center

**Step 2:** Change directory.

.. raw:: html

   <run></run>

.. code-block::

    cd ~/raphael-kit/c/2.1.3/

**Step 3:** Compile.

.. raw:: html

   <run></run>

.. code-block::

    gcc 2.1.3_TouchSwitch.c -lwiringPi

**Step 4:** Run.

.. raw:: html

   <run></run>

.. code-block::

    sudo ./a.out

While the code is running, the red LED lights up; when you tap on the touch switch module, the yellow LED turns on. 

.. note::

    If it does not work after running, or there is an error prompt: \"wiringPi.h: No such file or directory\", please refer to :ref:`install_wiringpi`.

**Code**

.. code-block:: c

    #include <wiringPi.h>
    #include <stdio.h>

    #define touchPin		   0
    #define led1		   3
    #define led2 		   2

    int main(void)
    {
        // When initialize wiring failed, print message to screen
        if(wiringPiSetup() == -1){
            printf(etup w"siringPi failed !");
            return 1; 
        }
        
        pinMode(touchPin, INPUT);
        pinMode(led1, OUTPUT);
        pinMode(led2, OUTPUT);
        
        while(1){
            // touch switch high, led1 on
            if(digitalRead(touchPin) == 1){
                digitalWrite(led1, LOW);
                digitalWrite(led2, HIGH);
                printf("You touch it! \r\n");
            }
            // touch switch low, led2 on
            if(digitalRead(touchPin) == 0){
                digitalWrite(led2, LOW);
                digitalWrite(led1, HIGH);
            }
        }

        return 0;
    }

**Code Explanation**

.. code-block:: c

    #define touchPin		   0
    #define led1		   3
    #define led2 		   2
    
Pin GPIO17, GPIO22 and GPIO27 of the T_Extension Board is corresponding to 
the GPIO0, GPIO3 and GPIO2 in wiringPi. Assign GPIO0, GPIO3 and GPIO2 to 
``touchPin``, ``led1`` and ``led2``. 

.. code-block:: c

    pinMode(touchPin, INPUT);
    pinMode(led1, OUTPUT);
    pinMode(led2, OUTPUT);

Set ``led1``, ``led2`` as output to write value to them and set ``touchPin`` as input to
read value from it.

.. code-block:: c

    while(1){
        // touch switch high, led1 on
            if(digitalRead(touchPin) == 1){
            digitalWrite(led1, LOW);
            digitalWrite(led2, HIGH);
            printf("You touch it! \r\n");
        }
        // touch switch low, led2 on
        if(digitalRead(touchPin) == 0){
            digitalWrite(led2, LOW);
            digitalWrite(led1, HIGH);
        }
    }

Set an infinite loop, when you tap on the touch switch module, ``touchPin`` is high, led1 will light up and print "You touch it!" . When touchPin is low, led2 will light up.


Phenomenon Picture
------------------------

.. image:: ../img/2.1.3touch_switch_module.JPG
    :width: 500
    :align: center